Re: If I were redoing git from scratch...

From: Shawn Pearce <spearce@spearce.org>
Date: Nov 4, 2006, 19:16 UTC
Message-ID: <20061104191651.GC2517@spearce.org>
In-Reply-To: <Pine.LNX.4.64.0611040829040.25218@g5.osdl.org>

Linus Torvalds <torvalds@osdl.org> wrote:

Show 7 quoted lines

> or for somebody who re-implements git in Java (where 
> performance isn't going to be the major issue anyway, and you probably do 
> "small" things like "commit" and "diff", and never do full-database things 
> like "git repack"), _then_ you can happily look at having something 
> fancier. Right now, it's too easy to just look at cumbersome interfaces, 
> and forget about the fact that those interfaces is sometimes what allows 
> us to practically do some things in the first place.

Yes and no.  :-)

As the only person here who has hacked on some of Git and also reimplemented the core on disk data structures in Java I can say I mostly agree with Linus.

Abstractions like the repository (to allow different GIT_DIRs to be used in the same process) isn't really a big deal and is not a large impact on performance. They could be implemented in the current C core.

But trying to abstractly represent an object in Java the same way that it is represented in Git costs a huge amount of memory. Java is at least 16 bytes of overhead per object, before you get to store anything in it. Translation: Linus is right, doing a real implementation of "git repack" in Java is nuts. It would barely be able to handle git.git, let alone linux.git or mozilla.git.